Note to Editors: The complete hurricane forecast and a detailed description of forecast factors are available on the Web at www.colostate.edu or at http://hurricane.atmos.colostate.edu.
At the halfway point of the 2005 hurricane season, following one of the most active early storm seasons on record in which Hurricane Katrina caused the greatest economic loss ever inflicted by a hurricane on the United States, William Gray and Philip Klotzbach of the Colorado State University hurricane forecast team are calling for very active storm activity to continue throughout September and October.
Gray and Klotzbach also continue to call for an above-average likelihood of landfalling hurricanes for the remainder of the hurricane season.
"Unfortunately, we are continuing the bad news by predicting above-average activity for September and October," said Gray. "This will be one of the most active seasons and is already the most destructive hurricane season on record."
Research data obtained through the end of August shows that the United States has already experienced 110 percent of the average full season tropical storm activity. In an average year, 33 percent of the seasonal average activity occurs by this date.
As detailed in a report issued this morning, the team’s September-only forecast calls for five named storms, four hurricanes and two major hurricanes. September is traditionally the most active month for hurricane activity. The October-only forecast, also issued today, predicts three named storms, two hurricanes and one major hurricane, also well above average.
August witnessed five named storms, two hurricanes and one intense hurricane, which is about 150 percent of average August storm activity.
As of Sept. 1, 12 named storms, four hurricanes and three major hurricanes have developed in the Atlantic basin. The long-term (1950-2000) average for an entire season is 9.6 named storms, 5.9 hurricanes and 2.3 intense hurricanes per year.
"The very active season we have seen to this point is far from over," said Klotzbach. "We expect that by the time the 2005 hurricane season is over, we will witness seasonal tropical cyclone activity at near-record levels."
As detailed in today’s updated Atlantic seasonal hurricane activity forecast, Gray and Klotzbach call for a total of 20 named storms to form in the Atlantic basin this year. Of these, 10 are predicted to become hurricanes and six are anticipated to evolve into intense hurricanes (Saffir/Simpson category 3-4-5) with sustained winds of 111 mph or greater. The total Net Tropical Cyclone (NTC) activity in 2005 is expected to be about 220 percent of the long-term average.
"This high forecast continues due to a variety of highly favorable tropical cyclone formation conditions," Klotzbach said. "Continued Atlantic Ocean warming, reduced vertical wind shear, low tropical Atlantic sea level pressures, increased West African rainfall and lack of El Nino conditions in the Pacific are some of the strongest factors driving this active season."
Another significant focus of the Colorado State team’s research involves efforts to develop forecasts of the probability of hurricane landfall along the U.S. coastline. The team has recently developed a methodology for calculating the probability of hurricane landfall along the entire U.S. coastline specifically for the months of September and October.
According to today’s report, for the month of September, there is a 43 percent chance of an intense hurricane hitting somewhere along the U.S. coastline (long-period average is 27 percent). For October, there is a 15 percent chance (long-period average is 6 percent).
Gray believes that, until last year, the United States had been very fortunate over the past four decades in witnessing very few major hurricanes making landfall in Florida and along the East Coast. This was due in large part to a combination of past climate conditions that did not favor major hurricane development or the tracking of these storms across the United States coastline. According to Gray, there has also been a degree of luck involved, as many major hurricanes have come close to the United States coastline and then veered away.
The last 10 years have witnessed 137 named storms, 77 hurricanes and 38 major hurricanes in the Atlantic basin. During that period – including 2004 where three major hurricanes made landfall – only six of the 38 major Atlantic basin hurricanes crossed the U.S. coastline. Based on historical averages, about one in three Atlantic basin major hurricanes comes ashore in the United States.
"As last year and the early part of this season make very clear, citizens living along the East and Gulf Coasts should continually be prepared for the possibility of landfalling hurricanes," said Gray.
The storm seasons spanning 1995-2004 comprised the most active 10 consecutive hurricane years on record, and the 2005 season has followed this active trend. The forecasters believe that the United States is in a new, multi-decadal era for increased storm activity.
"Our research indicates that the United States has entered an era of increased major hurricane activity which has been reflected in high activity during eight of the last 10 years," Klotzbach said. "We expect this active tropical cyclone era to likely span the next two or three decades."
The Colorado State forecast team does not attribute changes in recent or projected Atlantic basin hurricane activity to human-induced global warming. These changes in hurricane activity are viewed as resulting from long-period natural climate alterations that historical and paleo-climate records show to have occurred many times in the past.
Gray and Klotzbach will be issuing a seasonal update of their 2005 Atlantic basin hurricane activity forecast on Oct. 3.
Gray and Klotzbach continuously work to improve their forecast methodologies based on a variety of climate-related global and regional predictors. For a detailed description of the seasonal and monthly forecast factors, visit the Web at http://hurricane.atmos.colostate.edu.